How to configure DomainKeys DKIM for email authentication and is it still relevant?
Michael Ko
Co-founder & CEO, Suped
Published 19 Jun 2025
Updated 16 Aug 2025
7 min read
When delving into email authentication, understanding both historical and current protocols is crucial. DomainKeys and DomainKeys Identified Mail (DKIM) are central to this. While DKIM is the predominant standard today, the question of DomainKeys' relevance still surfaces, especially for those learning about email infrastructure or dealing with older systems. It is common to see people asking whether to configure DomainKeys alongside DKIM.
My experience has shown that many organizations, even large ones, might still have DomainKeys records in their DNS, leading to confusion. This isn't necessarily because they're actively using them, but often due to legacy configurations that were never fully removed when the transition to DKIM occurred. For modern email deliverability, the focus is almost entirely on DKIM.
This article will clarify the distinction between DomainKeys and DKIM, guide you through configuring DKIM for robust email authentication, and definitively address whether DomainKeys is still a necessary component in today's email landscape. We'll also touch upon how these protocols impact your overall email deliverability and sender reputation.
DomainKeys was an early email authentication protocol developed by Yahoo! to verify the sender of an email and ensure the message hadn't been altered in transit. It used cryptographic signatures added to the email header and a public key published in the sender's DNS records. While groundbreaking at the time, it had limitations.
DomainKeys Identified Mail (DKIM) emerged from DomainKeys and Cisco's Identified Internet Mail to create a more robust and widely adopted standard. DKIM also uses cryptographic signatures, but with enhancements that improved its security and flexibility. It is now one of the three pillars of email authentication, alongside SPF and DMARC.
The key difference lies in DKIM's ability to sign different parts of the email header and body, making it more resilient to minor modifications in transit. This enhanced integrity checking is vital for preventing email spoofing and phishing attacks. While DomainKeys laid the groundwork, DKIM perfected the approach, becoming the industry's preferred method for digitally signing emails.
DomainKeys (deprecated)
Origin: Developed by Yahoo! for email authentication.
Usage: Limited adoption, largely superseded by DKIM.
Policy Records: Required separate DNS TXT records for policy (e.g., k=rsa; t=y; p=publickey).
Current Relevance: Effectively obsolete, not checked by major email providers.
DKIM (current standard)
Origin: A fusion of DomainKeys and Identified Internet Mail.
Usage: Widely adopted industry standard.
Policy Records: Integrated into the DKIM record itself (e.g., v=DKIM1; k=rsa; p=publickey).
Current Relevance: Essential for email authentication and deliverability.
Configuring DKIM for email authentication
Configuring DKIM primarily involves generating a public-private key pair and publishing the public key in your domain's DNS as a TXT record. This setup allows recipient mail servers to verify that an incoming email, claiming to be from your domain, was indeed authorized by your domain's owner and hasn't been tampered with.
Step-by-step DKIM configuration
First, you need to generate a DKIM key pair. Most Email Service Providers (ESPs) or mail server software (like PMTA or OpenDKIM) will provide a utility for this. You'll get a public key and a private key. The private key stays on your sending server (MTA), while the public key is published in your DNS.
Next, you create a TXT record in your DNS. This record will be named something like selector._domainkey.yourdomain.com, where 'selector' is a unique name you choose (e.g., 'default', 'mail', or a date-based name). The value of this TXT record will be your public key, typically formatted with v=DKIM1; k=rsa; p=.... It's crucial that this record is configured correctly; Google Workspace and Microsoft 365 provide specific instructions.
Example DKIM DNS TXT RecordDNS
default._domainkey.yourdomain.com. IN TXT "v=DKIM1; k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA..."
Finally, ensure your mail server or ESP is configured to sign outgoing emails with your private key using the specified selector. After configuration, it's essential to test your DKIM setup to verify it's working correctly and that messages are being signed. You can use an email deliverability tester to check if your emails are properly DKIM-signed. Sometimes, a DKIM record can be configured but not signed by the email. Keep in mind that DKIM selector name examples are numerous, but the principle remains the same.
Is DomainKeys still relevant?
While DomainKeys was a precursor to DKIM, it is no longer relevant for modern email authentication. The standard was officially superseded by DKIM, and receiving mail servers, including major providers like Google and Yahoo, do not validate DomainKeys signatures anymore. This means that having a DomainKeys record (sometimes called a DomainKey policy record) in your DNS offers no benefit to your email deliverability or reputation.
Many legacy systems or outdated configurations might still generate DomainKeys signatures or have their DNS records published. However, these signatures are effectively ignored by modern email systems. Continuing to sign emails with DomainKeys, or maintaining its DNS records, is simply extra processing overhead and unnecessary bytes on the wire.
The only reason you might consider setting up DomainKeys (even for learning purposes) is within a private, controlled test environment using legacy software, as modern mail transfer agents (MTAs) and email providers no longer support it. For any live email sending, whether for corporate or marketing emails, your focus should be entirely on DKIM, SPF, and DMARC.
The importance of current email authentication
In the modern email ecosystem, robust authentication is non-negotiable. DKIM, alongside SPF and DMARC, forms the backbone of trusted email communication. These protocols work together to combat email spoofing, phishing, and other malicious activities, while simultaneously improving your sender reputation and email deliverability.
Misconfigurations or the absence of these records can lead to your emails being flagged as spam, rejected entirely, or even landing your sending IP or domain on a blocklist (or blacklist). The new requirements from major mailbox providers like Google and Yahoo further underscore the criticality of properly implemented DKIM domain alignment and DMARC.
My advice is to regularly review your authentication setup. Even small errors can have a significant impact on your inbox placement. Focusing your efforts on maintaining correct DKIM, SPF, and DMARC records is the most effective way to ensure your emails reach their intended recipients and maintain a strong sending reputation.
Maintaining robust email authentication
Ensuring your emails are properly authenticated is not a one-time setup; it's an ongoing process. Regularly check your DMARC reports to identify any authentication failures. These reports provide invaluable insights into how your emails are being perceived by receiving servers and can highlight issues with your SPF, DKIM, or DMARC configurations.
Views from the trenches
Best practices
Always prioritize DKIM, SPF, and DMARC. These are the modern standards that impact deliverability.
Use tools to test your DKIM configuration after any changes to ensure it's valid and applied.
Regularly monitor DMARC reports to identify and troubleshoot authentication failures.
Ensure your private key is secure and only accessible by authorized systems.
Common pitfalls
Attempting to implement DomainKeys on modern systems, which wastes effort and offers no benefit.
Assuming that just because a record exists, it's correctly configured or being used for signing.
Ignoring DMARC reports, missing critical insights into authentication issues.
Using short DKIM key lengths (e.g., 1024-bit) when 2048-bit keys are preferred for stronger security.
Expert tips
If your Mail Transfer Agent (MTA) allows DomainKey signing as a legacy option, it's best to disable it to avoid unnecessary processing.
Focus your learning on current email authentication protocols, as DomainKeys is no longer relevant for deliverability.
Even if large brands still have DomainKey signatures, it's likely due to inertia rather than active validation by recipients.
Don't rely on simply checking your email in Gmail; use a proper email authentication checker for detailed validation.
Expert view
Expert from Email Geeks says DomainKeys offers extra processing time and bytes on the wire, but it is not used by recipients, so its configuration is irrelevant for modern email systems.
2021-10-26 - Email Geeks
Expert view
Expert from Email Geeks says modern software typically does not support DomainKeys, and it is no longer validated by anyone.
2021-10-26 - Email Geeks
Key takeaways
While DomainKeys played a role in the evolution of email authentication, it has been largely superseded by DKIM. For current email deliverability and security, your efforts should be entirely focused on properly configuring DKIM, alongside SPF and DMARC. These three protocols are what mailbox providers rely on to verify your sending legitimacy and protect against malicious email practices.
Prioritizing these modern standards will significantly boost your chances of landing in the inbox, maintaining a healthy sender reputation, and ensuring your email communication is trusted. Avoid investing time in deprecated technologies like DomainKeys, as it provides no practical benefit in today's email landscape.
Yahoo! for email authentication.
Google and Yahoo, do not validate DomainKeys signatures anymore. This means that having a DomainKeys record (sometimes called a DomainKey policy record) in your DNS offers no benefit to your email deliverability or reputation.
